The present invention relates to a defect observation method and a device therefor in which defects or the like existing on or near a surface of a specimen detected by another defect inspection device are observed.
For example, existence of foreign substances on a semiconductor substrate (wafer) and pattern defects such as short circuits or disconnections (hereinafter, these are collectively described as defects) causes failure such as insulation failure or short circuits of wirings in a manufacturing process of a semiconductor device. With the advanced microfabrication of circuit patterns formed on a wafer, fine defects cause insulation failure of a capacitor and destruction of a gate oxide film or the like. These defects are mixed in various states due to various causes such as those generated from a movable part of a carrier device, generated from a human body, generated by reaction with process gas in a processing device, or mixed in chemicals or materials. Therefore, it is important in the mass production of semiconductor devices that defects generated during the manufacturing process are detected to quickly find out the cause of generation of the defects, and the generation of the defects is stopped.
As a conventional method of seeking the cause of generation of defects, there is a method in which the position of defects is first located by a defect inspection device, and the defects are observed and classified in detail by a review device using an SEM (Scanning Electron Microscope) to be compared with a database in which inspection results obtained in each manufacturing process are stored, so that the cause of generation of the defects is estimated.
In this case, the defect inspection device is an optical defect inspection device that illuminates light on the surface of a semiconductor substrate with a laser and carries out a dark-field observation of scattered light from defects to locate the position of the defects, or an optical appearance inspection device or an SEM inspection device that irradiates light of a lamp or laser or electron beams and detects a bright-field optical image of a semiconductor substrate to be compared with reference information, so that the position of the defects on the semiconductor substrate is located. Such observation methods are disclosed in Japanese Patent Application Laid-Open No. 2000-352697 or Japanese Patent Application Laid-Open No. 2008-157638.
As to a device that observes defects in detail using an SEM, U.S. Pat. No. 6,407,373 describes such a method and a device that using positional information of defects on a specimen detected by another inspection device, the position on the specimen is detected by an optical microscope mounted in the SEM defect observation device and the positional information of defects obtained by detecting with the another inspection device is amended, so that the defects are observed (reviewed) in detail by the SEM defect observation device.
Further, Japanese Patent Application Laid-Open No. 2007-225563 describes optical high-resolution detection using a super-resolution technique by illumination of stationary waves.
Further, Japanese Patent Application Laid-Open No. 2011-106974 describes that the sensitivity of a dark-field optical microscope is increased by arranging a filter having spatial distribution on or near a pupil plane of a detection optical system.
A general optical microscope has a resolution limit caused by a diffraction limit proportional to the wavelength of light due to the wave nature of light. For example, in the case where light having a wavelength of 532 nm is collected by an aplanatic lens with an NA of 0.5, the resolution limit becomes 649 nm. A super-resolution technique is a method of obtaining a high degree of spatial resolution exceeding the resolution limit that is dependent on the wavelength.
As a super-resolution technique, there is a near-field microscopy in which scattered light from evanescent waves that locally exist only near the surface of a specimen are detected when light is irradiated, and a stimulated emission suppression microscopy in which a laser having a wavelength different from that of an excitation laser to emit light of fluorescent molecules and that of a doughnut-shaped excitation laser surrounding the excitation laser is irradiated. However, the near-field optical microscopy is technically difficult, and further the throughput is slow. The stimulated emission suppression microscopy is a microscopy used to capture the light emission of fluorescent. Thus, in the case where a high degree of throughput is required, the stimulated emission suppression microscopy is not used in the present situation when the fluorescent molecules are not observed.
Further, an SIM (Structured illumination Microscopy) using structured illumination with the intensity spatially modulated has recently drawn attention, and fluorescent microscopes using the SIM are sold by Carl Zeiss Inc. and Nikon Corporation. Further, a dark-field SIM is disclosed in Japanese Patent Application Laid-Open No. 2007-225563. The SIM is relatively high in throughput as compared to a near-field optical microscope because a wider area can be irradiated.
With the advanced microfabrication of circuit patterns in response to the needs of high integration in recent manufacturing of LSIs, the sizes of target defects become smaller. In response to this, the dimensions of defects to be detected by an optical defect inspection device are required to be smaller. Under the circumstances, the wavelength of illumination is shortened, the resolution is increased, and the NA (Numerical Aperture) of a detection lens is increased in the optical defect inspection device. There are limitations to the shortening of the wavelength of illumination in the device. As a method of increasing the NA of the detection lens, there is a metamaterial having a negative liquid immersion and a negative refractive index. However, it is difficult to use the liquid immersion in a semiconductor inspection, and it is technically difficult to put the metamaterial to practical use. In the super-resolution technique using the structured illumination, the phase of illumination is modulated, plural signals having different intensity phases are obtained, and the resolution can be improved on the basis of changes of the obtained signals. However, as a detection target becomes smaller in size, it becomes difficult to increase the resolution by the super resolution. Because in the case where signals from the detection target are buried in background noise, changes of the signals from the detection target cannot be captured.
In Japanese Patent Application Laid-Open No. 2000-352697, Japanese Patent Application Laid-Open No. 2008-157638, U.S. Pat. No. 6,407,373, and Japanese Patent Application Laid-Open No. 2011-106974, an observation of defects by an optical microscope using a super-resolution technique is not described. On the other hand, Japanese Patent Application Laid-Open No. 2007-225563 describes a super-resolution technique in which two light fluxes are allowed to interfere with each other on a plane of a specimen to illuminate stationary waves and scattered light is detected so that changes of nanometer-order scattered light is detected. However, Japanese Patent Application Laid-Open No. 2007-225563 does not describe that as in the case of detecting minute defects on a semiconductor substrate, scattered light from minute defects are detected while being separated from background noise generated by nanometer-order minute irregularities on a surface of a specimen.
Accordingly, in order to solve the problems of the conventional technique, the present invention provides a defect observation method and a device therefor in which minute defect signals that are likely to be buried in background noise can be detected while being separated from the background noise, so that much smaller defects on a specimen can be observed.